willis



May 20. 1924. 1,495,@59

E. D. WILLIS INTEROFFICE TRUNK CIRCUITS FOR TELEPHONE SYSTEMS Filed June18 1920 Patented May 20, 1924.

UNITED STATES PATENT OFFICE.

BERNARD D. WILLIS, 01? OAK PARK, ILLINOIS, AESIGNOR 'lO AU'IOMATICELECTRIC COMPANY, 01! CHICAGO, ILLINOIS, A. CORPORATION OF ILLINOIS.

INTEROFFTGE TRUNK GTRG'UI'JS IFOR TELEPHONE SYSTEME}.

Application filed June 18, 1920. Serial No. 389,820.

the invention is the provision of an i1n-- proved automatic to manualtrunk circuit which is particularly useful for temporarily connectingautomatic and n'lanual offices dur ing a cut over from one system to theother, or -for permanently connecting such ol'lices when automatic andmanual systems serving the same territory are consolidated.

Trunk circuits of the above character are not broadly new, and theinvention necessarily consists in certain principles oi operation whichare thought to be new, and in the various circuit improvements employedfor carrying out these principles.

The invention will be described with reference to the accompanyingdrawing which is a circuit diagram o'l an intero'lTice trunk circuitembodying the principles of the invcntiou.

Referring to the drawing, the reference characters 80 and 31 indicatethe two conductors of an inter-oliice trunk line. This trunk lineextends from the so called repeater it which is located in an autonnu'icother. to an answering jack J at an A. operators position in a manualo'l'licc, and is one oi": a group of similar trunk lines which areprovided to handle the trailic irom the automatic olllce to the manualoliicc. Another group of trunk lines, of a different type, is providedfor handling traffic .in the other direction, but with these othertrunks the present invention is not concerned. In order to give theautomatic subscribers access to the trunk lines extending to the manualoliice these trunk lines are multipled in the banks of selector switchesin the usual manner. Thus the trunk line shown in the drawing may bereached by way of bank contacts 2, 8, and 4 which may be located in thebank of a first selector switch, being coimected in multiple to similarcontacts in the banks of the other first selectors in the automaticoflice. The automatic switches are of the well known Strowger verticaland rotary type, operated according to the well known two wire system ofcontrol such as disclosed in U. S. Patent No. 1,281,112, granted to B.D. Willis, October 8, 1918, and the repeater E is provided to establisha holding circuit for any selector which is operated to establishconnection with the trunk line associated therewith. This is inaccordance with the usual practice and is done primarily to avoid thenecessity of having three conductors be tween offices.

As stated before, the answering jack J is located at an A operatorsposition in the manual oilice. The particular A operator in front ofwhom this jack appears may handle trunked calls exclusively, or thejacks associated with the incoming trunks from the automatic oflice maybe distributed among a plurality of operators positions. In. any case,the trucked calls are handled substantially like local calls originatingin the manual. oflice and the ope alter, or operators, have uniformsupervision. Cord circuits such as disclosed in the fourth edition ofAmerican Telephone Practice, on page 315, may be used. The group ofrelays indicated by the reference character F are the trunk relays, arelocated at the manual oflice, and their functions and operations will bedescribed fully hereinafter.

For this purpose it will be assumed that a subscriber in the automaticol'lice desires to obtain connection with a subscriber in the manualmiles, and the process or setting up the connection will be described.When the receiver is removed the calling line is extended by means oi?an individual line or trunk selecting switch to an idle first selectorswitch in the usual and well known manner. The manual subscribers mayhave full tclepl'ione numbers listed in the directory, the first digitin each number being the oilice digit, and the remaining digitscorresponding to the location of the line in the multiple at the manualofiice, and the calling subscriber will now operate his calling deviceter the first digit in the desired number. By this means the firstselector is directively controlled to raise its shaft step by step untilthe wipers stand opposite the level which is reserved for the trunksextending to the desired manual office. At the end of the verticalmovement of the selector the rotary trunk selecting movement isinitiated automatically and the wipers are rotated step by step insearch of an idle trunk line. Assuming that the trunk line shown in thedrawing is the first idle trunk line, when the wipers arrive at bankcontacts 2, 3, and 4 the rotary movement will cease and by the operationof the switching relay in the selector the calling line will be extendedby way of the selector line wipers, bank contacts 2 and l, andconductors 16 and 18 to the upper and lower windings, respectively, ofthe double wound line relay 5 of the repeater E.

Upon the extension of the calling line as above described the line relay5 is energized over the line circuit and closes a circuit for theslowacting release relay 6 at its armature '9. Upon energizing, relay 6closesa holding circuit which may be traced from ground G by way of theleft hand winding of induction coil R, normally closed contact springscontrolled by armature 13, working contact of armature l0 and the saidarmature, release trunk conductor 17, test contact 3, test wiper of theoperated first selector, and the winding of the switching relay in saidselector to battery. This circuit serves to maintain the selector inoperated position during the call and it may be added that a branch ofthe above circuit performs the same function for the subscribersindividual line switch. It will be understood also that the groundpotential on test contact 3 extends to multiple test contacts in thebanks of other selector switches thereby rendering the trunk line busy.

The calling subscriber may now operate his calling device in accordancewith the remaining digits of the desired number. As a result the linerelay 5 is deenergized a plurality of times for each digit, but withouteffect, and the digits are wasted. The A operator at the manualexchange, however, has already been signaled. lVhen relay 6 pulls up itcloses a bridge across trunk conductors 30and'3l which includes theright hand Winding of induction coil R and the winding of relay 7. Itfollows that relay 7 will be energized in series with relays 33 and 34at the manual exchange, the latter two relays being bridged across thetrunk line in series with the battery. Upon energizing, relay 7 groundsthe holding circuit direct at its armature 13 and thus cuts out the lefthand Winding of the induction coil R. At the manual exchange the relays33 and 34 jointly close a circuit for the answering or call signal lampL. At the same time relay 34L connects up a lead from the ringingmachine RM. Condenser 51 is of very low capacity, preferably about .006F., and permits just enough ringing current to leak back through thereceiver at the calling station to give the calling subscriber the usualringing current induction. This arrangement is customary in automaticsystems and is provided here for the sake ol uniformity. Hearing thesignal, the calling subscriber will understand that the desired line isbeing signalled and will wait on the line, although, as a matter offact, the ringing machine has nothing to do with the signallingoperation that has actually been performed.

When the operator sees the lighted answering lamp L, she will understandthat a call has been received over the associated trunk line and willrespond by plugging into the jack J with an idle cord circuit. Thislights the supervisory lamp in the cord circuit and energizes the sleeverelay 35. llela y 35, upon energizing, prepares a locking circuit forrelay 36 at its armature 4-1, and at its armat-ures l3 and asdisconnects relays 33 and 34: from the trunk line. This causes theanswering lamp L to be extinguished, and also disconnects the ringingmachine RM. At the same time relay 7 at the repeater E deenergizes andconnects the left hand win ling of repeating coil R into the holdingcircuit agam.

The operator will now threw her listening key and will note whether ornot there is a discriminating tone on the line. This operation isnecessary of course only in case acharge is made for inter-oflicc calls,which the operator is required to record. Any subscriber whose credit ispoor and who .is to be denied inter-ofiice service on that account hashis individual line switch circuit so arranged that a distinctive.audible (one is placed on the holding circuit whenever a call isattempted. This tone is transferred to the line at the repeater E bymeans of the repeating coil R and when heard by the operator issullicient authority for her to refuse to complete the connection.lle'leronce is made at this time to my U. Patent No. 1,281,112, grantedOct. 8, 1918, which shows and describes in full an arrangemeni of thiskind. In order to proceed with the explanation we will assume that notone is heard by the operator when she comes in on the line, which meansthat the calling subscriber is entitled to service. The oper ator willtherefore obtain the desired number from the calling subscriber and willproceed to complete the connection with the other end of her cordcircuit, either directly or with the assistance of a B operator,depending on the particular type of manual exchange in use. Theconnection having been established the operator will actuate key Kmomentarily and need pay no further attention to the call, unlessrecalled by the supervisory signals in the cord.

lVhcn key K is operated a circuit is closed for relay 37 which, uponenergizing, closes Inc iii)

1,&96,059 3 a circuit for relay 36 at armature 4Z9- Upon energizing,relay 36 looks itself at armature 4.7 and at armature L6 prepares acircuit for relay 34. In addition to closing the circuit of relay 36,relay 37 connects its upper winding in shunt oi condenser 52 by means ofits armature 4L8. Condenser 52 is included in the upper conductor of thetrunk line, normally preventing current flow from the cord circuit; andit follows that when the condenser is shunted by the winding of relay37, the said relay will be locked up by current flow over a circuitwhich includes the battery at the cord circuit and the relay 7 at therepeater E. Relay 7 is accordingly energized again to cut out the lefthand winding of induction coil R, and at the cord circuit thesupervisory relay is energized to put out the supervisory lamp. It maybe mentioned also that relay 7 disconnects the condenser which isnormally bridged around its winding in order to give a good circuit forthe distinctive tone, when the tone is on the line.

The complete connection has now been established and when the calledsubscriber in. the niianual o'iiice answers the conversation can begin.

When the subscribers are through talking they will both replace theirreceivers. When the called. subscriber hangs up the operator is giventhe usual disconnect supervision at the calling end of the cord circuit.lVhen the calling subscriber hangs up the line relay at the repeater Eis permanently deenergized and falls back to break the circuit of theslow acting release relay 6. The latter relay then deenergizes also, theholding circuit is broken, and the first selector and individual lineswitch are released. Relay 6 also opens the bridge across the trunkconductors 30 and 31 at the repeater and relay 7 and the supervisoryrelay in the answering end of the operators cord circuit aredeenergized. The latter relay permits the answering supervisory lamp tobe lighted also and the operatornow has a disconnect signal at both ends01'' her cord circuit. At the same time that the supervisory relay fallsback the relay 37 deenergizes and thereby disconnects its upper windingfrom in shunt oi condenser 52. Relay 36, however, remains locked up.

The operator may now pull down the con nection and it she does so relaysand 36 will be deenergized and all the apparatus will be in normalposition. However, in order to complete the explanation, we will assumethat another call is received over the same trunk line before theoperator has had time to disconnect. Sometimes, especially during rushhours, the operators are rather slow at pulling down connections, andthis may well occur. When the second calling subscriber connects withthe trunk line the line and release relays 5 and 6 are energized asbefore and the bridge including relay 7 is closed across the trunk lineat the out going side of the repeater E. As a result a circuit is closedfor relay 3 11, which is now connected to the upper line conductor byway of armatures 43, L6, and i8, tor although relay 33 is disconnected,the lower line conductor goes to battery at the manual exchange,nevertheless, because the cord is still up. i

The supervisory relay at the cord. circuit is included in the lowertalking strand, which goes to the ungrounded pole oi battery and itfollows that relays 34L and 7 and the supervisory relay in the cord willbe energized in series. This puts out the supervisory lamp and removesone of the disconnect signals. Relay 34 being new operated th circuit ofthe answering lamp L is closed but since relay 33 is at normal the lampcircuit will he closed through the interrupter I. This causes the lampto flash which is more effective in recalling the operator than apermanent signal would be.

On perceiving the flashing line lamp th operator will replug in order torestore the circuits to the usual call. received condition: That is, shewill withdraw the plug from jack J for an. instant in order todeenergize relays 36 ant When the plug is reinserted relay 35 will pullup again, but not relay 36, and relay 34, which falls back when the plugis withdrawn, will remain deenergized. The circuits are now in the samecondition as they were in the case previously described, when the trunkline was first taken for use, and the operator will proceed according tothe usual routine.

Although it is not essential, I have shown a test jack J which isprovided for the convenience of a switchboard man or other employee intesting the trunk circuit. These test jacks may be mounted on the, relayraclrs in the terminal room and afford ready access to the trunkcircuits. lVhen the jack J connected with, a telephone or other testingdevice is bridged across the two upper springs oi the jack while the twolower springs are short circuited. The latter operation energizes relay32 which pulls up and opens the two sides of: the trunk line, leavingthe test telephone bridged across the line in the direction of theoperator. The person testing can now tall: to the operator and ascertainii. the trunk line is working or not. Relay 32 also connects theungrounded pole of battery to the upper trunk conductor 30. Relay 6 atthe repeater E being at normal, relay 7 is now energized by current flowover the upper trunk conductor and at its armature 12 connects ground tothe release trunk conductor 17. This renders the trunk line busy. Itwill be understood that if the trunk circuit should get out of order sothat it would become necessary toestablish a more permanent busycondition, the lower springs of the test jack can be short circuited bymeans of any small metallic object which may be left in place until thecircuit is repaired.

Having described my invention what I consider to be new and desire tohave protected by Letters Patent will be pointed out in the appendedclaims.

What I claim as my invention is:

1. In a telephone system, a trunk line extending to an operatorsposition, means whereby a calling subscriber can connect with said trunkline, a call signal at the operators position, means for operating saidsignal steadily when the call is received, means at the operatorsposition for connecting said trunk line with a called line, meanswhereby the calling subscriber can disconnect from said trunk line, andmeans whereby it a. second connection to said trunk line is establishedby a calling subscriber before the trunk line is disconnected from thecalled line the said call signal will be operated intermittently.

2. In a telephone system, a trunk circuit terminating in a jack at anoperators position, means including automatic selectively movableswitches whereby a calling sub-- scriber can extend a connection to saidtrunk line, a call signal lam at th operators position and means forcausing the same to glow steadily when the connection to said trunk isestablished, means whereby the operator can connect said trunk line witha called line, means whereby the calling subscriber can release saidswitches, and means for flashing said call signal lamp in case a secondcalling subscriber should connect with said trunk line before theoperator has disconnected the same from the called line.

3. In a telephone system, a trunk line connecting automatic and manualexchanges, means including automatic switcheswhereby a calling automaticsubscriber can connect with said trunk line, a repeater in said. trunkline for closing a holding circuit tor'said switches and for closing abridge across the outgoing side of said trunk line, a relay and abattery normally in bridge of said trunk line at the manual exchange,the said relay being actuated when the first bridge is closed to signalthe operator, means for disconnecting said second bridge when theoperator plugs in to answer the call, a condenser in one'conductor ofsaid trunk line preventing current flow from the operators cord circuit,a relay in said first bridge which is deenergized when the second bridgeis cut off, a signalling device for indicating the character of thecalling line connected in inductive relation to the trunk line to givethe operator an audible signal when said second relay falls back, and akey actuated by the operator for short circuiting said condenser,whereby the said second, relay is energized by current from theoperators cord circuit and the said signalling device is renderedinoperative.

4. In a telephone system, a trunk line extending to an operatorsposition, means whereby a calling subscriber can connect with said trunkline, a call signal at the operators position, a pair of relays in saidtrunk line, means dependent upon the condition of said trunk line fordctern'iining whether one or both of said relays will be operated when acall is received, means responsive to the operation of only one of saidrelays causing the intermittent operation of said signal, and meansresponsive to the operation of both of said relays causing the steadyoperation of said signal.

In a telephone system, lines of different classes, an operators switchboard, a trunk line terminating in a jack on said switch board, a cordcircuit at said switch board, means including an automatic switchadapted to be set under the control ol any calling subscriber forconnecting such subscribers line to said trunk line, meansautoinatically responsive to the insertion of the plug of said cordcircuit in said jack for signalling the operator over said trunk line toindicate the class ot the calling line. said signalling means includinga relay at the seized end of said trunk line for stopping the signallingoperation, and a circuit controlled by the operator at said switch boardfor energizing said relay and maintaining the same energized to permitconversation with the calling subscriber.

6. In a telephone system, lines of different classes, an operatorsswitch board, a trunk line terminating in a jack on said switch board, acord circuit at said switch board, means including an automatic switchadapted to be set under the control of any calling subscriber forconnecting such subscribers line to said trunk line, class signallingmeans associated with the seized end of said trunk line, means includinga relay energized when the trunk is seized and automatically deenergizedresponsive to the insertion oi the cord circuit plug in said jack forrendering said signalling means effective to indicate the class of thecalling line to the operator, and means controlled by the operatorthereafter for again energizing said relay to stop the signallingoperation.

7. In a telephone system, lines of different classes, an operatorsswitch board, a trunk line terminating in a jack on said switch board, acord circuit at said switch board, means including an automatic switchadapted to be set under the control of any calling subscriber forconnecting such subscribers line to said trunk line, class signallingmeans associated with the seized end of said trunk line, a batterybridged across said trunk line at the switch board end thereof, a relaybridged across the seized end of said trunk line and responsive tocurrent from said battery to render said signalling means inefi'ective,means for disconnecting said battery from in bridge oi the trunk lineresponsive to the insertion of the cord circuit plug in said jack,thereby deenergizing said relay to permit said. signalling means tobecome effective to indicate the class of the calling line to the openator, and a circuit established thereafter under operator control forsupplying current to said relay from said cord circuit, whereby therelay is again energized to render the signalling means ineffective.

8. In a telephone system, a trunk line extending to an operatorsposition, means whereby a calling subscriber can connect with said trunkline, a call signal at the operators position, means for operating saidsignal in one manner when the call is received, means at the operatofisposition for connecting said trunk line with a called line, meanswhereby the calling subscriber can disconnect from said trunk line, andmeans whereby if a second connection to said trunk line is establishedby a calling subscriber before the trunk line is disconnected from thecalled line the said call signal will be operated in a dilferent manner.

Signed by me at Chicago, Cook County, Illinois, this 11th day of June,1920.

BERNARD D. WILLIS.

